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#ifndef SHARE_GC_G1_G1MONITORINGSUPPORT_HPP
#define SHARE_GC_G1_G1MONITORINGSUPPORT_HPP
#include "gc/shared/collectorCounters.hpp"
#include "gc/shared/generationCounters.hpp"
#include "services/memoryManager.hpp"
#include "services/memoryService.hpp"
#include "runtime/mutex.hpp"
class CollectorCounters;
class G1CollectedHeap;
class HSpaceCounters;
class MemoryPool;
// Class for monitoring logical spaces in G1. It provides data for
// both G1's jstat counters as well as G1's memory pools.
//
// G1 splits the heap into heap regions and each heap region belongs
// to one of the following categories:
//
// * eden : regions that have been allocated since the last GC
// * survivors : regions with objects that survived the last few GCs
// * old : long-lived non-humongous regions
// * humongous : humongous regions
// * free : free regions
//
// The combination of eden and survivor regions form the equivalent of
// the young generation in the other GCs. The combination of old and
// humongous regions form the equivalent of the old generation in the
// other GCs. Free regions do not have a good equivalent in the other
// GCs given that they can be allocated as any of the other region types.
//
// The monitoring tools expect the heap to contain a number of
// generations (young, old, perm) and each generation to contain a
// number of spaces (young: eden, survivors, old). Given that G1 does
// not maintain those spaces physically (e.g., the set of
// non-contiguous eden regions can be considered as a "logical"
// space), we'll provide the illusion that those generations and
// spaces exist. In reality, each generation and space refers to a set
// of heap regions that are potentially non-contiguous.
//
// This class provides interfaces to access the min, current, and max
// capacity and current occupancy for each of G1's logical spaces and
// generations we expose to the monitoring tools. Also provided are
// counters for G1 concurrent collections and stop-the-world full heap
// collections.
//
// Below is a description of how the various sizes are calculated.
//
// * Current Capacity
//
// - heap_capacity = current heap capacity (e.g., current committed size)
// - young_gen_capacity = current max young gen target capacity
// (i.e., young gen target capacity + max allowed expansion capacity)
// - survivor_capacity = current survivor region capacity
// - eden_capacity = young_gen_capacity - survivor_capacity
// - old_capacity = heap_capacity - young_gen_capacity
//
// What we do in the above is to distribute the free regions among
// eden_capacity and old_capacity.
//
// * Occupancy
//
// - young_gen_used = current young region capacity
// - survivor_used = survivor_capacity
// - eden_used = young_gen_used - survivor_used
// - old_used = overall_used - young_gen_used
//
// Unfortunately, we currently only keep track of the number of
// currently allocated young and survivor regions + the overall used
// bytes in the heap, so the above can be a little inaccurate.
//
// * Min Capacity
//
// We set this to 0 for all spaces.
//
// * Max Capacity
//
// For jstat, we set the max capacity of all spaces to heap_capacity,
// given that we don't always have a reasonable upper bound on how big
// each space can grow. For the memory pools, we make the max
// capacity undefined with the exception of the old memory pool for
// which we make the max capacity same as the max heap capacity.
//
// If we had more accurate occupancy / capacity information per
// region set the above calculations would be greatly simplified and
// be made more accurate.
//
// We update all the above synchronously and we store the results in
// fields so that we just read said fields when needed. A subtle point
// is that all the above sizes need to be recalculated when the old
// gen changes capacity (after a GC or after a humongous allocation)
// but only the eden occupancy changes when a new eden region is
// allocated. So, in the latter case we have minimal recalculation to
// do which is important as we want to keep the eden region allocation
// path as low-overhead as possible.
class G1MonitoringSupport : public CHeapObj {
friend class VMStructs;
friend class G1MonitoringScope;
G1CollectedHeap* _g1h;
// java.lang.management MemoryManager and MemoryPool support
GCMemoryManager _incremental_memory_manager;
GCMemoryManager _full_gc_memory_manager;
MemoryPool* _eden_space_pool;
MemoryPool* _survivor_space_pool;
MemoryPool* _old_gen_pool;
// jstat performance counters
// incremental collections both young and mixed
CollectorCounters* _incremental_collection_counters;
// full stop-the-world collections
CollectorCounters* _full_collection_counters;
// stop-the-world phases in G1
CollectorCounters* _conc_collection_counters;
// young collection set counters. The _eden_counters,
// _from_counters, and _to_counters are associated with
// this "generational" counter.
GenerationCounters* _young_gen_counters;
// old collection set counters. The _old_space_counters
// below are associated with this "generational" counter.
GenerationCounters* _old_gen_counters;
// Counters for the capacity and used for
// the whole heap
HSpaceCounters* _old_space_counters;
// the young collection
HSpaceCounters* _eden_space_counters;
// the survivor collection (only one, _to_counters, is actively used)
HSpaceCounters* _from_space_counters;
HSpaceCounters* _to_space_counters;
// When it's appropriate to recalculate the various sizes (at the
// end of a GC, when a new eden region is allocated, etc.) we store
// them here so that we can easily report them when needed and not
// have to recalculate them every time.
size_t _overall_committed;
size_t _overall_used;
size_t _young_gen_committed;
size_t _old_gen_committed;
size_t _eden_space_committed;
size_t _eden_space_used;
size_t _survivor_space_committed;
size_t _survivor_space_used;
size_t _old_gen_used;
// It returns x - y if x > y, 0 otherwise.
// As described in the comment above, some of the inputs to the
// calculations we have to do are obtained concurrently and hence
// may be inconsistent with each other. So, this provides a
// defensive way of performing the subtraction and avoids the value
// going negative (which would mean a very large result, given that
// the parameter are size_t).
static size_t subtract_up_to_zero(size_t x, size_t y) {
if (x > y) {
return x - y;
} else {
return 0;
}
}
// Recalculate all the sizes.
void recalculate_sizes();
void recalculate_eden_size();
public:
G1MonitoringSupport(G1CollectedHeap* g1h);
~G1MonitoringSupport();
void initialize_serviceability();
MemoryUsage memory_usage();
GrowableArray memory_managers();
GrowableArray memory_pools();
// Unfortunately, the jstat tool assumes that no space has 0
// capacity. In our case, given that each space is logical, it's
// possible that no regions will be allocated to it, hence to have 0
// capacity (e.g., if there are no survivor regions, the survivor
// space has 0 capacity). The way we deal with this is to always pad
// each capacity value we report to jstat by a very small amount to
// make sure that it's never zero. Given that we sometimes have to
// report a capacity of a generation that contains several spaces
// (e.g., young gen includes one eden, two survivor spaces), the
// mult parameter is provided in order to adding the appropriate
// padding multiple times so that the capacities add up correctly.
static size_t pad_capacity(size_t size_bytes, size_t mult = 1) {
return size_bytes + MinObjAlignmentInBytes * mult;
}
// Recalculate all the sizes from scratch and update all the jstat
// counters accordingly.
void update_sizes();
void update_eden_size();
CollectorCounters* conc_collection_counters() {
return _conc_collection_counters;
}
// Monitoring support used by
// MemoryService
// jstat counters
// Tracing
// Values may not be consistent wrt to each other.
size_t young_gen_committed() { return _young_gen_committed; }
size_t eden_space_used() { return _eden_space_used; }
size_t survivor_space_used() { return _survivor_space_used; }
size_t old_gen_committed() { return _old_gen_committed; }
size_t old_gen_used() { return _old_gen_used; }
// Monitoring support for MemoryPools. Values in the returned MemoryUsage are
// guaranteed to be consistent with each other.
MemoryUsage eden_space_memory_usage(size_t initial_size, size_t max_size);
MemoryUsage survivor_space_memory_usage(size_t initial_size, size_t max_size);
MemoryUsage old_gen_memory_usage(size_t initial_size, size_t max_size);
};
// Scope object for java.lang.management support.
class G1MonitoringScope : public StackObj {
TraceCollectorStats _tcs;
TraceMemoryManagerStats _tms;
public:
G1MonitoringScope(G1MonitoringSupport* g1mm, bool full_gc, bool all_memory_pools_affected);
};
#endif // SHARE_GC_G1_G1MONITORINGSUPPORT_HPP